Transparent, UV resistant, thermoformable film made from crystallizable thermoplastics, its use and process for its production

ABSTRACT

The invention relates to a transparent, UV-stabilized, single or multi-layered thermoformable film which contains, as a principal constituent, a crystallizable thermoplastic, preferably polyethylene terephthalate, and at least one UV-stabilizer. The inventive films are characterized by having a good stretchability, thermoformability and good optical and mechanical properties. Said films are suitable for outdoor uses just like shaped bodies made of the same.

Transparent, UV-resistant, thermoformable film made from crystallizablethermoplastics, its use and process for its production.

The invention relates to a transparent, UV-resistant, thermoformablefilm made from crystallizable thermoplastics, the thickness of which ispreferably in the range from 10 to 500 μm. The film comprises at leastone UV stabilizer as light stabilizer and has good orientability, goodthermoformability, and very good optical and mechanical properties. Theinvention further relates to the use of this film and to a process forits production.

BACKGROUND OF THE INVENTION

Transparent films made from crystallizable thermoplastics with athickness from 1 to 500 μm are well known.

These films are not thermoformable and do not comprise any UVstabilizers as light stabilizers. Neither the films nor the items ormoldings produced from them are therefore suitable for outdoorapplications. Even after a short period in outdoor applications, thesefilms and moldings exhibit yellowing and impairment of mechanicalproperties due to photooxidative degradation by sunlight.

EP-A-0 620 245 describes films with improved heat resistance. Thesefilms comprise antioxidants suitable for scavenging free radicals formedin the film and for degrading any peroxide formed. However, thatspecification makes no proposal as to how the UV resistance of films ofthis type may be improved. Nor does that specification state whetherthese films are suitable for thermoforming processes.

It is an object of the present invention, therefore, to provide atransparent, thermoformable film with a thickness which is preferablyfrom 10 to 500 μm and which, in addition to good orientability, goodmechanical properties, and also good optical properties, in particularhas high UV resistance and thermoformability.

High UV resistance means that the films are not damaged, or are damagedonly to an extremely small degree, by sunlight or by other UV radiation,and therefore the films and moldings produced from them are suitable foroutdoor applications and/or critical indoor applications. In particularafter a number of years of outdoor use the films should not yellow orshow embrittlement or surface-cracking, nor show any impairment ofmechanical properties. High UV resistance therefore means that the filmabsorbs UV light and transmits light only when the visible range hasbeen reached.

Examples of good optical properties are high light transmittance (>84%),high surface gloss (>120), extremely low haze (<20%), and low YellownessIndex (YI<10).

Examples of good mechanical properties are high modulus of elasticity(E_(MD)>3200 N/mm²; E_(TD)>3500 N/mm²), and also good values for tensilestress at break (in MD>100 N/mm²; in TD>130 N/mm²).

Good orientability includes the ability of the film during itsproduction to give excellent orientation in both longitudinal andtransverse directions, without break-offs. An example of adequatethermoformability is the ability of the film to be thermoformed oncommercially available thermoforming machinery without uneconomicpredrying, to give complex and large-surface-area moldings.

The film of the invention should also be recyclable, in particularwithout loss of optical or mechanical properties, so that it can also beused for short-lived products and in the construction of exhibitionstands, for example.

BRIEF DESCRIPTIONS OF THE INVENTION

The object of the invention is achieved by way of a transparentthermoformable film having a thickness which is preferably from 10 to500 μm, and comprising, as the main constituent, a crystallizablethermoplastic, and characterized in that the film comprises at least oneUV stabilizer as light stabilizer.

The film has preferably been mono- or biaxially oriented.

DETAILED DESCRIPTION OF THE INVENTION

The transparent film comprises, as main constituent, a crystallizablethermoplastic. According to the invention, crystallizable thermoplasticsare crystallizable homopolymers, e.g. polyesters, polyolefins, orpolyamides; crystallizable copolymers, e.g. polyethyleneterephthalate/isophthalate, polyethylene terephthal/naphthalate;crystallizable compositions; crystallizable recycled material, and othertypes of crystallizable thermoplastics.

Preferred suitable crystallizable or semicrystalline thermoplastics arepolyesters such as polyethylene terephthalate, polybutyleneterephthalate, polyethylene naphthalate, preferably polyethyleneterephthalate (PET). It is also possible to use a mixture ofcrystallizable thermoplastics. The crystallinity of the thermoplasticsis preferably in the range from 5 to 65%.

The transparent film may be either single-layer or multilayer. Thetransparent film may also have been coated with various copolyesters oradhesion promoters.

Light, in particular the ultraviolet content of solar radiation, i.e.the wavelength region from 280 to 400 nm, induces degradation inthermoplastics, as a result of which their appearance changes due tocolor change or yellowing, and there is also an adverse effect onmechanical/physical properties.

Inhibition of this photooxidative degradation is of considerableindustrial and economic importance, since otherwise there are drasticlimitations on the applications of many thermoplastics.

The absorption of UV light by polyethylene terephthalates, for example,starts at below 360 nm, increases markedly below 320 nm and is verypronounced at below 300 nm. Maximum absorption occurs at between 280 and300 nm.

In the presence of oxygen it is mainly chain cleavage which occurs, butthere is no crosslinking. The predominant photooxidation products inquantity terms are carbon monoxide, carbon dioxide and carboxylic acids.Besides the direct photolysis of the ester groups, consideration has tobe given to oxidation reactions which likewise form carbon dioxide, viaperoxide radicals.

In the photooxidation of polyethylene terephthalates there can also becleavage of hydrogen at the position a to the ester groups, givinghydroperoxides and decomposition products of these, and this may beaccompanied by chain cleavage (H. Day, D. M. Wiles: J. Appl. Polym. Sci16, 1972, p. 203).

UV stabilizers, i.e. light stabilizers which are UV absorbers, arechemical compounds which can intervene in the physical and chemicalprocesses of light-induced degradation. Carbon black and other pigmentscan give some protection from light. However, these substances areunsuitable for transparent films, since they cause discoloration orcolor change. The only compounds suitable for transparent matt films arethose organic or organometallic compounds which produce no, or onlyextremely slight, color or color change in the thermoplastic to bestabilized, that is to say they are soluble in the thermoplastic.

For the purposes of the present invention, UV stabilizers suitable aslight stabilizers are those which absorb at least 70%, preferably 80%,particularly preferably 90%, of the UV light in the wavelength regionfrom 180 to 380 nm, preferably from 280 to 350 nm. These areparticularly suitable if they are thermally stable in the temperaturerange from 260 to 300° C., that is to say they do not decompose and donot cause release of gases. Examples of UV stabilizers suitable as lightstabilizers are 2-hydroxybenzophenones, 2-hydroxybenzotriazoles,organonickel compounds, salicylic esters, cinnamic ester derivatives,resorcinol monobenzoates, oxanilides, hydroxybenzoic esters, andsterically hindered amines and triazines, and among these preference isgiven to the 2-hydroxybenzotriazoles and the triazines.

The UV stabilizer(s) is (are) preferably present in the outer layer(s).The core layer may also have UV stabilizer, if required.

It was highly surprising that the use of the abovementioned UVstabilizers in films gave the desired result. The skilled worker wouldprobably first have attempted to achieve a certain degree of UVresistance by way of an antioxidant, but would have found that the filmrapidly yellows on weathering.

In the knowledge that UV stabilizers absorb UV light and thereforeprovide protection, the skilled worker would be likely to have usedcommercially available UV stabilizers. He would then have observed that

-   -   the UV stabilizer has unsatisfactory thermal stability and at        temperatures of from 200 to 240° C. decomposes and releases        gases, and    -   large amounts (from about 10 to 15% by weight) of the UV        stabilizer have to be incorporated so that the UV light is        absorbed and the film therefore not damaged.

At these high concentrations it would have been observed that the filmis already yellow just after it has been produced, with Yellowness Indexdeviations (YI) around 25. It would also have been observed that itsmechanical properties are adversely affected. Orientation would haveproduced exceptional problems, such as

-   -   break-offs due to unsatisfactory strength, i.e. modulus of        elasticity too low,    -   die deposits, causing profile variations,    -   roller deposits from the UV stabilizer, causing impairment of        optical properties (defective adhesion, nonuniform surface), and    -   deposits in stretching frames or heat-setting frames, dropping        onto the film.

It was therefore more than surprising that even low concentrations ofthe UV stabilizer achieve excellent UV protection. It was verysurprising that, together with this excellent UV protection:

-   -   within the accuracy of measurement, the Yellowness Index of the        film is unchanged from that of an unstabilized film;    -   there were no releases of gases, no die deposits and no frame        condensation, and the film therefore has excellent optical        properties and excellent profile and layflat, and    -   the UV-stabilized film has excellent stretchability, and can        therefore be produced in a reliable and stable manner on        high-speed film lines at speeds of up to 420 m/min.

It is moreover very surprising that it is also possible to reuserecycled material without any adverse effect on the Yellowness Index ofthe film.

It is significant for the invention that the crystallizablethermoplastic has a diethylene glycol content (DEG content) of ≧1.0% byweight, preferably ≧1.2% by weight, in particular ≧1.3% by weight,and/or a polyethylene glycol content (PEG content) of ≧1.0% by weight,preferably ≧1.2% by weight, in particular ≧1.3% by weight, and/or anisophthalic acid content (IPA) of from 3 to 10% by weight.

In one particularly preferred embodiment, the film of the inventioncomprises from 0.01 to 5.0% by weight of2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxyphenol of the formula

or from 0.01 to 5.0% by weight of2,2-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,2,2-tetramethylpropyl)phenolof the formula

In one preferred embodiment, it is also possible to use mixtures ofthese two UV stabilizers or mixtures of at least one of these two UVstabilizers with other UV stabilizers, the total concentration of lightstabilizer preferably being from 0.01 to 5% by weight, based on theweight of crystallizable polyethylene terephthalate.

It was more than surprising that, by virtue of higher diethylene glycolcontent and/or polyethylene glycol content and/or IPA content than instandard thermoplastics, the films can be thermoformed cost-effectivelyon commercially available thermoforming plants and give excellentreproduction of detail.

The surface gloss of the films of the invention, measured to DIN 67530(measurement angle 20°), is greater than 120, preferably greater than140, and the light transmittance L, measured to ASTM D 1003, is morethan 84%, preferably more than 86%, and the haze of the film, measuredto ASTM D 1003, is less than 20%, preferably less than 15%, surprisinglygood for the UV resistance achieved.

The standard viscosity SV (DCA) of the polyethylene terephthalate,measured in dichloroacetic acid to DIN 53728, is preferably from 600 to1000, with preference from 700 to 900. The crystalline melting pointmeasured by DSC at a heating rate of 10° C./min is preferably in therange from 220 to 280° C.

The polyethylene terephthalate (PET) preferably has a diethylene glycolcontent (DEG content) and/or polyethylene glycol content (PEG content)15 greater than 1.3% by weight, in particular >1.5% by weight. In oneparticularly preferred embodiment, the DEG content and/or PEG content isfrom 1.6 to 5% by weight. According to the invention, the max. DEGand/or PEG content is about 5.0% by weight.

It is surprising here that oriented PET films can be thermoformed byvirtue of a diethylene glycol content and/or polyethylene glycol contenthigher than in standard polyester.

The thermoforming process generally encompasses the steps of predrying,heating, molding, cooling, demolding, conditioning. Surprisingly, in thethermoforming process it was found that the films of the invention canbe thermoformed without prior predrying. This advantage drasticallyreduces the costs of the forming process in comparison withthermoformable polycarbonate films or thermoformable polymethylmethacrylate films, for which, depending on thickness, predrying timesof from 10 to 15 hours are required at from 100 to 120° C.

The film of the invention, preferably a PET film, comprising at leastone UV stabilizer, may be single-layer or multilayer.

In the multilayer embodiment, the film has a structure of at least onecore layer and at least one outer layer, and particular preference isgiven here to a three-layer structure of type A-B-A or A-B-C. Thethicknesses of the outer layers are preferably from 0.5 to 2 μm.

A substantive factor for the multilayer embodiment is that the DEGcontent and/or PEG content and the standard viscosity of thecrystallizable thermoplastic, e.g. the polyethylene terephthalate, ofthe core layer are similar to those of the polyethylene terephthalate orthe thermoplastic of the outer layer(s) which is (are) adjacent to thecore layer.

In one particular embodiment, the outer layers may also be composed of apolyethylene naphthalate homopolymer or of a polyethyleneterephthalate-polyethylene naphthalate copolymer, or of a composition.

In this embodiment, the thermoplastics of the outer layers likewise havestandard viscosity similar to that of the thermoplastic, e.g. thepolyethylene terephthalate, of the core layer.

In the multilayer embodiment, the UV stabilizer is preferably present inthe outer layer(s). However, the core layer may also have UV stabilizersif necessary.

Unlike in the single-layer embodiment, the concentration of thestabilizer(s) here is based on the weight of thermoplastic in the layerwhich has stabilizer(s). Here, again, preferred concentrations are from0.01 to 5.0% by weight.

Very surprisingly, weathering tests to the test specification of ISO4892 using the Atlas Ci65 Weather-Ometer showed that in the case of athree-layer film the provision of UV stabilizers in the outer layers offrom 0.5 to 2 μm in thickness is fully sufficient to improve UVresistance.

The UV-stabilized films having more than one layer and produced viaknown coextrusion technology are therefore of major commercial interestwhen compared with fully UV-resistant monofilms, since less UVstabilizer is needed to give comparable UV resistance.

There may also be provision, on at least one side of the film, of ascratch-resistant coating, a copolyester or an adhesion promoter.

Weathering tests have shown that, even after from 5 to 7 years in anoutdoor application (extrapolated from the specific weathering tests),the UV-stabilized films of the invention generally show no increase inyellowing, no embrittlement, no loss of surface gloss, no surfacecracking and no impairment of mechanical properties.

During production of the film of the invention it was also found thatthe UV-stabilized film can readily be oriented longitudinally andtransversely without break-offs. In addition, no releases of gases ofany type from the UV stabilizer were found during the productionprocess. This is very advantageous, since most UV stabilizers evolveunpleasant gases at extrusion temperatures above 260° C., and aretherefore of no use.

The film of the invention or the molding may moreover readily berecycled without polluting the environment and without loss ofmechanical properties, and the film is therefore suitable for use asshort-lived advertising placards, for example, or other promotionalitems.

The film may, furthermore, be thermoformed without predrying, andcomplete moldings may therefore be produced therefrom.

Examples of parameters found for the thermoforming process were asfollows.

Step of process Film of invention Predrying Not required Moldtemperature ° C. 100-160 Heat time <5 sec per 10 μm of thickness Filmtemperature 160-200 during shaping ° C. Possible orientation factor 1.5-2.0 Reproduction of detail Good Shrinkage % <1.5

One way of producing the film of the invention is by an extrusionprocess on an extrusion line.

The light stabilizer may be added before the material leaves theproducer of the thermoplastic polymer, or may be metered in to theextruder during film production.

The DEG and/or PEG content of the polyethylene terephthalate areadvantageously established by the producer of the raw material, duringthe polymerization process.

Adding the light stabilizer by way of masterbatch technology isparticularly preferred. The light stabilizer is dispersed in a solidcarrier material. Solid carrier materials which may be used are thethermoplastic itself, e.g. the polyethylene terephthalate, or else otherpolymers sufficiently compatible with the thermoplastic.

In masterbatch technology it is important that the particle size and thebulk density of the masterbatch are similar to the particle size and thebulk density of the thermoplastic, so that homogeneous distribution andthus homogeneous UV resistance can be achieved.

The inventive films may be produced by known processes for example froma polyester with, where appropriate, other raw materials and with the UVstabilizer, and/or with other customary additives in customary amountsof from 0.1 to a maximum of 10% by weight, either in the form of amonofilm or else in the form of, where appropriate coextruded, filmshaving more than one layer and with identical or differently constructedsurfaces, where one surface may, for example, have been pigmented but nopigment is present at the other surface. Known processes may also havebeen used to provide one or both surfaces of the film with aconventional functional coating.

In the preferred extrusion process for producing an inventive polyesterfilm, the molten polyester material is extruded through a slot die andquenched on a chill roll, in the form of a substantially amorphousprefilm. This amorphous prefilm is then reheated and stretchedlongitudinally and transversely, or transversely and longitudinally, orlongitudinally, transversely and again longitudinally and/ortransversely. In general, the stretching temperatures are from T_(g)+10°C. to T_(g)+60° C. (where T_(g) is the glass transition temperature),the longitudinal stretching ratio is usually from 2 to 6, in particularfrom 3 to 4.5, and the transverse stretching ratio is from 2 to 5, inparticular from 3 to 4.5, and the ratio for any second longitudinalstretching carried out is from 1.1 to 3. The first longitudinalstretching may, where appropriate, be carried out simultaneously withthe transverse stretching (simultaneous stretching). This is followed bythe heat-setting of the film at oven temperatures of from 200 to 260°C., in particular from 220 to 250° C. The film is then cooled and woundup.

The surprising combination of excellent properties makes the transparentfilm of the invention, and moldings produced therefrom, highly suitablefor a variety of applications, e.g. for interior decoration, forconstructing exhibition stands, for exhibition requisites, for displays,for placards, for protective glazing of machines or vehicles, in thelighting sector, in fitting out shops or stores, or as a promotionalrequisite or laminating material.

Due to its good UV resistance, the transparent film of the invention isalso suitable for outdoor applications, e.g. for greenhouses, roofingsystems, exterior cladding, protective coverings, applications in theconstruction sector or illuminated advertising profiles.

Due to its thermoformability, the film of the invention is suitable forthermoforming any desired moldings for indoor or outdoor applications.

Examples are used below to describe the invention in more detail.

The following standards and methods are used here when testingindividual properties.

Test Methods

DIN=Deutsches Institut fur Normung [German Institute forStandardization] ISO=International Organization for Standardization

DEG Content/PEG Content/IPA Content

DEG/PEG/IPA content is determined by gas chromatography aftersaponification in methanolic KOH and neutralization with aqueous HCl.

Surface Gloss

Surface gloss is measured with a measurement angle of 20° to DIN 67530.

Light Transmittance

For the purposes of the present invention, the light transmittance isthe ratio of total light transmitted to the amount of incident light.

Light transmittance is measured using “®Hazegard plus” test equipment toASTM D 1003.

Haz

Haze is that percentage proportion of the transmitted light whichdeviates by more than 2.5° from the average direction of the incidentlight beam. Clarity is determined at an angle of less than 2.5°.

Haze is measured using “Hazegard plus” apparatus to ASTM D 1003.

Surface Defects

Surface defects are determined visually.

Mechanical Properties

Modulus of elasticity, tear strength and elongation at break aremeasured longitudinally and transversely to ISO 527-1-2.

SV (DCA) and IV (DCA)

Standard viscosity SV (DCA) is measured by a method based on DIN 53726in dichloroacetic acid.

Intrinsic viscosity (IV) is calculated as follows from the standardviscosity (SV)IV(DCA)=6.67·10⁻⁴ SV(DCA)+0.118Weathering (on Both Sides) and UV Resistance

UV resistance is tested as follows to the test specification of ISO 4892

Test equipment Atlas Ci65 Weather-Ometer Test conditions ISO 4892, i.e.artificial weathering Irradiation time 1000 hours (per side) Irradiation0.5 W/m², 340 nm Temperature 63° C. Relative humidity 50% Xenon lampInternal and external filter made from borosilicate Irradiation cycles102 minutes of UV light, then 18 minutes of UV light with water sprayonto the specimens, then another 102 minutes of UV light, etc.Yellowness Index

Yellowness Index YI is the deviation from the colorless condition in the“yellow” direction and is measured to DIN 6167. Yellowness Index values(YI)<5 are not visible.

In the examples and comparative examples below each of the films is atransparent film of different thickness, produced on the extrusion linedescribed.

Each of the films was first weathered to the test specification of ISO4892 for 1000 hours per side, using an Atlas Ci65 Weather-Ometer, andthen tested for mechanical properties, discoloration, surface defects,haze and gloss.

EXAMPLES Example 1

A transparent film of 50 μm thickness is produced, comprisingpolyethylene terephthalate as principal constituent, 0.3% by weight ofSylobloc, and 1.0% by weight of the UV stabilizer2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxyphenol (®Tinuvin 1577from Ciba-Geigy).

Tinuvin 1577 has a melting point of 149° C. and is thermally stable upto about 330° C.

To obtain homogeneous distribution, 0.3% by weight of Sylobloc and 1.0%by weight of the UV stabilizer are incorporated directly into thepolyethylene terephthalate at the premises of the producer of the rawmaterial.

The polyethylene terephthalate from which the transparent film isproduced has a standard viscosity SV (DCA) of 810, corresponding to anintrinsic viscosity IV (DCA) of 0.658 dl/g, and has a DEG content of1.6% by weight and a PEG content of 1.7% by weight.

The 50 μm monofilm is produced by the extrusion process described.

The transparent PET film produced has the following property profile:

Thickness 50 μm Surface gloss, (Measurement angle 20°) Side 1 155 Side 2152 Light transmittance 91% Haze 4.0% Surface defects per m² noneLongitudinal modulus of elasticity 3700 N/mm² Transverse modulus ofelasticity 4900 N/mm² Longitudinal tensile stress at break 120 N/mm²Transverse tensile stress at break 200 N/mm² Yellowness Index (YI) 3.1

After 1000 hours of weathering per side using an Atlas Ci65Weather-Ometer, the PET film has the following properties:

Thickness 50 m Surface gloss, Side 1 145 (Measurement angle 20°) Side 2141 Light transmittance 90.1% Haze 4.5% Surface defects per m² none(cracks, embrittlement) Yellowness Index (YI) 3.6 Longitudinal modulusof elasticity 3650 N/mm² Transverse modulus of elasticity 4850 N/mm²Longitudinal tensile strength 110 N/mm² at break Transverse tensilestrength 200 N/mm² at break

Example 2

Using a method based on Example 1, a transparent film is produced, theUV stabilizer 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxyphenol(®Tinuvin 1577) being added in the form of a masterbatch. Themasterbatch is composed of 5% by weight of ®Tinuvin 1577 as activecomponent and 95% by weight of the polyethylene terephthalate fromExample 1.

Prior to extrusion, 90% by weight of the polyethylene terephthalate fromExample 1 are dried with 10% by weight of the masterbatch for 5 hours at170° C. Extrusion and film production take place by a method based onExample 1.

The transparent PET film produced has the following property profile:

Thickness 50 μm Surface gloss, Side 1 160 (Measurement angle 20°) Side 2157 Light transmittance 91.3% Haze 3.8% Surface defects noneLongitudinal modulus of elasticity 3600 N/mm² Transverse modulus ofelasticity 4800 N/mm² Longitudinal tensile stress 110 N/mm² at breakTransverse tensile stress at break 190 N/mm² Yellowness Index (YI) 3.4

After 1000 hours of weathering per side using an Atlas Ci65Weather-Ometer, the PET film has the following properties:

Thickness 50 μm Surface gloss, Side 1 148 (Measurement angle 20°) Side 2146 Light transmittance 89.9% Haze 4.1% Surface defects none YellownessIndex (YI) 4.3 Longitudinal modulus of elasticity 3500 N/mm² Transversemodulus of elasticity 4700 N/mm² Longitudinal tensile stress at 100N/mm² break Transverse tensile stress at break 170 N/mm²

Example 3

Using a method based on Example 2, a transparent film of thickness 350μm is produced. The PET film produced has the following propertyprofile:

Thickness 350 μm Surface gloss, Side 1 149 (Measurement angle 20°) Side2 144 Light transmittance 84.1% Haze 13.1% Surface defects per m² noneYellowness Index 4.5 Longitudinal modulus of elasticity 3100 N/mm²Transverse modulus of elasticity 3600 N/mm² Longitudinal tensile stressat 110 N/mm² break Transverse tensile stress at break 190 N/mm²

After 1000 hours of weathering per side using an Atlas Ci65Weather-Ometer, the PET film has the following properties:

Thickness 350 μm Surface gloss, Side 1 136 (Measurement angle 20°) Side2 131 Light transmittance 84.3% Haze 14.0% Surface defects (cracks, noneembrittlement) Yellowness Index (YI) 5.4 Longitudinal modulus ofelasticity 3050 N/mm² Transverse modulus of elasticity 3500 N/mm²Longitudinal tensile stress at 100 N/mm² break Transverse tensile stressat break 160 N/mm²

Example 4

Coextrusion technology is used to produce a multilayer PET film of 50 μmthickness with the layer sequence A-B-A, B being the core layer and Abeing the outer layers. The thickness of the core layer B is 48 μm andthat of each of the two outer layers which cover the core layer is 1 μm.

The polyethylene terephthalate used for the core layer B is identicalwith that from Example 1, except that it comprises no Sylobloc®. Thepolyethylene terephthalate of the outer layers A is identical with thepolyethylene terephthalate from Example 1, i.e. the raw material for theouter layers has 0.3% by weight of Sylobloc.

Using a method based on Example 2, the 5% strength by weight ®Tinuvin1577 masterbatch is used, but 20% by weight of the masterbatch areadded, by way of masterbatch technology, only to the outer layers of 1μm thickness.

The transparent multilayer PET film produced, with UV-resistant outerlayers, has the following property profile:

Layer structure A-B-A Total thickness 50 μm Surface gloss, Side 1 164(Measurement angle 20°) Side 2 159 Light transmittance 94.2% Haze 2.1%Surface defects none Longitudinal modulus of elasticity 3750 N/mm²Transverse modulus of elasticity 4950 N/mm² Longitudinal tensile stress130 N/mm² at break Transverse tensile stress at break 210 N/mm²Yellowness Index (YI) 2.9

After 1000 hours of weathering per side using an Atlas Ci65Weather-Ometer, the multilayer film has the following properties:

Layer structure A-B-A Total thickness 50 μm Surface gloss, Side 1 152(Measurement angle 20°) Side 2 150 Light transmittance 92.3% Haze 3.0%Surface defects none Longitudinal modulus of elasticity 3550 N/mm²Transverse modulus of elasticity 4800 N/mm² Longitudinal tensile stress115 N/mm² at break Transverse tensile stress at break 185 N/mm²Yellowness Index (YI) 3.0

The inventive examples show that the optical and mechanical propertiesof the films meet the high requirements set, while at the same time UVresistance has been substantially increased.

The films from Examples 1-4 may be thermoformed without predrying toproduce moldings on commercially available thermoforming machinery, e.g.from the company Illig. The reproduction of detail in the moldings isexcellent, and the surface is uniform.

Comparative Example 1

Using a method based on Example 1, a PET monofilm of 50 μm thickness isproduced. Unlike in Example 1, no UV stabilizer is present in the film.The PET used has a conventional DEG content of 0.6% by weight andcomprises no PEG.

The unstabilized transparent film produced has the following propertyprofile:

Thickness 50 μm Surface gloss, Side 1 160 (Measurement angle 20°) Side 2155 Light transmittance 91.8% Haze 3.6% Surface defects noneLongitudinal modulus of elasticity 4350 N/mm² Transverse modulus ofelasticity 5800 N/mm² Longitudinal tensile stress 185 N/mm² at breakTransverse tensile stress at break 270 N/mm² Longitudinal tensile strain160% at break Transverse tensile strain at break 80% Yellowness Index(YI) 2.7

The film has inadequate thermoformability.

After 1000 hours of weathering per side using an Atlas Ci65Weather-Ometer, the film has surface cracks and embrittlement phenomena.It therefore becomes impossible to measure any accurate propertyprofile, in particular mechanical properties. In addition, the filmexhibits visible yellowing.

1. A transparent, oriented thermoformable film comprising acrystallizable thermoplastic or a mixture of different crystallizablethermoplastics and at least one UV stabilizer, said crystallizablethermoplastic comprising at least one of either diethylene glycol orpolyethylene glycol present in an amount of greater than or equal to1.0% by weight.
 2. The film as claimed in claim 1, characterized in thatthe thermoplastic has a crystallinity of from about 5 to about 65%. 3.The film as claimed in claim 1, characterized in that the thermoplasticcomprises a polyester.
 4. The film as claimed in claim 1, characterizedin that the thermoplastic comprises polyethylene terephthalate,polybutylene terephthalate or polyethylene naphthalate.
 5. The film asclaimed in claim 4, characterized in that the thermoplastic comprisespolyethylene terephthalate.
 6. The film as claimed in claim 4,characterized in that the thermoplastic consists essentially ofpolyethylene terephthalate having a diethylene glycol content or apolyethylene glycol content or a diethylene glycol content and apolyethylene glycol content of more than about 1.3% by weight.
 7. Thefilm as claimed in claim 4, characterized in that the thermoplasticconsists essentially of polyethylene terephthalate having a diethyleneglycol content or a polyethylene glycol content or a diethylene glycolcontent and a polyethylene glycol content of from about 1.6 to about 6%by weight.
 8. The film as claimed in claim 5, characterized in that thepolyethylene terephthalate has a standard viscosity SV (DCA) of fromabout 600 to about
 1000. 9. The film as claimed in claim 1, wherein theUV stabilizer comprises 2-hydroxybenzotriazoles or triazines or mixturesof these UV stabilizers.
 10. The film as claimed in claim 1, wherein theUV stabilizer comprises2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol or2,2′-methylenebis-6-(2H-benzotriazol-2-yl)-4-(1,1,2,2-tetramethylpropyl)phenolor mixtures of these UV stabilizers or mixtures of these UV stabilizerswith others.
 11. The film as claimed in claim 1, wherein theconcentration of the UV stabilizer or UV stabilizers is from about 0.01to about 5% by weight, based on the weight of the layer of thecrystallizable thermoplastic or thermoplastics.
 12. The film as claimedin claim 1, wherein the film has two or more layers.
 13. The film asclaimed in claim 12, wherein the UV stabilizer is present in the outerlayer or layers.
 14. The film as claimed in claim 1, wherein the filmhas a thickness of from about 1 to about 500 μm.
 15. The film as claimedin claim 1, wherein the film is biaxially oriented.
 16. The film asclaimed in claim 5, wherein the polyethylene terephthalate has acrystallite melting point, measured by DSC with a heating rate of 10°C./min, of from about 220 to about 280° C.
 17. The film as claimed inclaim 5, wherein the polyethylene terephthalate has a crystallizationtemperature, measured by DSC with a heating rate of 10° C./min, of fromabout 75 to about 280° C.
 18. The film as claimed in claim 12, whereinthe outer layer or outer layers comprise polyethylene naphthalate. 19.The film as claimed in claim 12, wherein the outer layer or outer layer,comprise copolymers or compounds made from polyethylene terephthalateand polyethylene naphthalate.
 20. A process for producing a film amclaimed in claim 1, comprising the steps of melting a crystallizablethermoplastic or a mixture made from crystallizable thermoplastic in anextruder together with at least one UV stabilizer, extruding the melt toyield a prefilm, orienting the prefilm to yield a biaxially orientedfilm, and heat setting the biaxially oriented film.
 21. The process asclaimed in claim 20, wherein the UV stabilizer or a mixture containingthe UV stabilizer is added by way of masterbatch technology.
 22. Amethod of making a molding comprising transforming a film as claimed inclaim 1 into a molding.
 23. A molding comprising a film as claimed inclaim
 1. 24. A transparent, oriented thermoformable film comprising acrystallizable thermoplastic or a mixture of different crystallizablethermoplastic and at least one UV stabilizer, said crystallizablethermoplastic including a glycol composition comprising a mixture of adiethylene glycol and polyethylene glycol, said diethylene glycolpresent in an amount of greater than or equal to 1.0% by weight and saidpolyethylene glycol present In an amount of greater than or equal to1.2% by weight, wherein said glycol composition includes a greateramount of polyethylene glycol than diethylene glycol.
 25. A transparent,biaxially oriented thermoformable film comprising a crystallizablethermoplastic or a mixture of different crystallizable thermoplasticsand at least one UV stabilizer, said thermoplastic consistingessentially of polyethylene terephthalate having at least one of eithera diethylene glycol content or a polyethylene glycol content of morethan about 1.3% by weight, said film formed using a single-steplongitudinal orientation.